In general, liquid such as the highly-refined chemicals for semiconductors or the general chemical agents is filled in a container such as a glass bottle or a polyethylene tank in a production plant, and is shipped in a state in which a lid is attached to an opening formed on this container for filling and taking out. As a method of taking out liquid stored in such a container, a siphon tube system which introduces gas such as air into the interior of the container and delivers the liquid out of the container by the pressure of the gas is known.
In this system, the lid attached to the opening for filling and taking-out (hereinafter, referred to as “container inlet port”) is removed, and then a plug having a siphon tube and a gas supply channel which serves as a liquid flow channel is attached to the opening of the container inlet port. Then, a socket to which a tube for taking out the liquid and a tube for introducing the gas can be connected independently is fitted into the plug, so that a primary flow channel for taking out the liquid and a secondary flow channel for introducing the gas are formed in the plug and socket attached to the opening of the container inlet port (for example, see Japanese Unexamined Patent Application, Publication No. 2002-59993).